1. The Field of the Invention
This application relates generally to fasteners. More specifically, the present invention relates to a medical fastener that can shorten in length and increase in width over time.
2. The Relevant Technology
Bones are a vital skeletal feature and provide the frame and structural support for holding associated muscles and other tissue. Additionally, bones, such as the skull bones and ribs, are responsible for protecting vital organs such as the brain, heart lungs, and the like. While bones are structurally strong, they tend to break for various reasons when subjected to excessive forces. Usually, the healing process includes a medical professional aligning the bones on each side of the break so that the regenerated bone material provides a structurally sound mended bone.
In addition to aligning the bone, various stabilizing techniques have been used to retain the broken bone in proper alignment during the healing process. Traditionally, casts have been used to stabilize minor breaks that do not need structural reinforcement at the bone. On the other hand, some complicated fractures or breaks can be susceptible to falling out of alignment during the healing process. As such, plates and fasteners can be used to stabilize the broken bones or fix bone structures. Use of these kinds of structural reinforcement systems during healing have been known to provide bone regeneration and mending.
Due to excellent strength and stability profiles, metallic fasteners and plates have dominated the market for reinforcing breaks or fractures during healing. The most accepted metallic fasteners and plates are biocompatible titanium and/or titanium alloys; however, other types of metallic materials have also been used. Nevertheless, metallic fasteners and plates can be problematic and have some disadvantages
One disadvantage of implanted metallic fasteners and plates arises from being treated as a foreign body, which sometimes requires the fasteners and plates to be removed. This can occur even if the metallic fastener and plate system is initially well tolerated. As such, the subsequent surgery to remove the metallic fastener and plate system can cause additional trauma to the patient, and adds additional costs to the health care system; especially when the patient has to be hospitalized after the procedure. Additionally, if the metallic fastener and plate system includes an iron component, the irons released from the metallic implant may be found in other organs, which can cause long-term problems.
Another major disadvantage of metallic fastener and plate systems arises from being much stronger than the bone being supported. As such, a broken bone that is fixed with a metallic fastener and plate system may not experience proper loading during the healing process. This is because the metallic repair system can carry a large portion of the load that is normally carried by the bone. As a result, the bone can become weaker over time when the metallic repair system is left in place. Accordingly, after removal of the metallic repair system, the repaired bone may be susceptible to fracturing around the region that was previously supported. Even though the metallic repair system provides structural reinforcement to the healing bone, the bone may develop decreased stability.
Additional problems arise because bone is a living structure. When a metallic fastener is drilled into bone, the compact pressure that results, for example, on a plate, is very high and leads to very good initial stability. Under the stress exerted by the fastener and the plate, the bone will change its structure and the fastener may loosen over time. This causes significant problems with maintaining bone alignment during bone regeneration because the plate can move as the fastener loosens.